1. Field of the Invention
The present invention relates to a method of manufacturing a plate member and a plate member.
2. Description of the Related Art
Conventionally, as a method of processing main faces of a plate member, a method in which a grinding device that grinds the main faces of the plate member in a planar shape by using a whetstone is used is disclosed (for example, see Japanese Patent Application Laid-Open (JP-A) No. 2002-86354).
Meanwhile, as a method of manufacturing a glass plate that is a plate member made of glass, a heating and stretching method in which a base glass plate having a predetermined thickness is heated so as to be softened and is stretched so as to have a desired thickness in the longitudinal direction is disclosed (for example, see JP-A No. 11-199255 and JP-A No. 2004-67393).
On the other hand, in order to cover the surface of a solar cell module, for a used glass plate, a texture process in which a concave-convex shape having a fine pitch is formed on the surface of the used glass plate is performed so as to decrease reflectivity of the surface, whereby the conversion efficiency of the solar cell module is improved (for example, see Takahashi Kiyoshi et al., “Photovoltaic Generation”, Morikita Publication, 1979, p 153).
Here, as described in JP-A No. 2004-67393, in a glass plate manufactured by using the heating and stretching method, there is a case where the main face is curved in a concave shape so as to decrease the thickness in the center portion in the width direction and increase the thickness the most in the end portion. In order to use such a glass plate having a low flatness due to the curvature of the main faces for the purpose of requiring a high flatness such as a semiconductor device substrate, a spacer used in a flat panel display of the field-effect type, or a magnetic disk substrate, the main faces thereof need to be processed so as to increase the flatness thereof.
A glass plate manufactured by using a conventional heating and stretching method will be further described in detail. FIG. 39 is a perspective cross-sectional view of a glass plate manufactured by using the conventional heating and stretching method, cut in a face perpendicular to the longitudinal direction thereof. As shown in FIG. 39, this glass plate 51 has main faces 51a and 51b facing each other and facets 51c and 51d facing each other in the width direction. The facets 51c and 51d are approximately parallel to each other in the longitudinal direction. However, the main faces 51a and 51b are curved in a concave shape such that a thickness t31 in the center portion in the width direction is small, and a thickness t32 in the end portion is the largest. Accordingly, the flatness of the glass plate is low. Such a difference between the thickness of the center portion and the end portion is thought to be caused by different flow speeds of the glass material in the center portion and the end portion at the time of softening the base glass plate so as to be stretched.
Accordingly, conventionally, as shown in FIG. 40, a glass plate 52 having a high flatness of the main faces is manufactured having by cutting off both end portions 51e and 51f of the glass plate 51 and polishing the curved portions 51g to 51j of the main faces 51a and 51b. As a result, when the glass plate 52 is manufactured, a portion of the glass plate 51 to be wasted is increased. Accordingly, the manufacturing cost is increased, and the number of manufacturing processes such as a cutting process or a polishing is increased or the processing time is increased. Therefore, there is a problem in that the manufacturing cost is increased.
In contrast, a method of decreasing the curvature of the main surfaces by adjusting the temperature distribution inside a stretching heating furnace used in a stretching and heating process is disclosed (see JP-A No. 8-183627).